Flutter 'List' 不是类型转换中类型 'String' 的子类型

Question

在 flutter 中，我应该为服务器端应用程序制作这个 json 结构:

{
  "data": [
    {
      "staff_id": "barcode1",
      "class_id": "session_id1",
      "class_name": "session_name1",
      "enter_date": "enter_date1",
      "Exit_date": "exit_date1",
      "username": "username1"
    },
    {
      "staff_id": "barcode2",
      "class_id": "session_id2",
      "class_name": "session_name2",
      "enter_date": "enter_date2",
      "Exit_date": "exit_date2",
      "username": "username2"
    }
  ]
}

我实现这个结构的代码:

class RestData{
  final List<Data> data;
  RestData({@required this.data});

  Map<String, dynamic> toJson() => {
    'data':data
  };
}

class Data {
  final String staff_id;
  final String class_id;
  final String class_name;
  final String enter_date;
  final String exit_date;
  final String username;

  Data({this.staff_id,this.class_id,this.class_name,this.enter_date,this.exit_date,this.username});

  Data.fromJson(Map<String, dynamic> json)
      : staff_id = json['staff_id'],
        class_id = json['class_id'],
        class_name = json['class_name'],
        enter_date = json['enter_date'],
        exit_date = json['exit_date'],
        username = json['username'];

  Map<String, dynamic> toJson() {
    var map = new Map<String, dynamic>();
    map["staff_id"] = staff_id;
    map["class_id"] = class_id;
    map["class_name"] = class_name;
    map["enter_date"] = enter_date;
    map["exit_date"] = exit_date;
    map["username"] = username;

    return map;
  }
}

//--------------------------------------

List<Data> list = [];

for (int i = 0; i < barcodes.length; i++) {
  list.add(Data(staff_id: 'aaa', class_id: '1111', class_name: '2222', enter_date: '3333', exit_date: '444444', username: '5555'));
}

结果:

restData = {RestData} 
 data = {_GrowableList} size = 1
  0 = {Data} 
   staff_id = "aaa"
   class_id = "1111"
   class_name = "2222"
   enter_date = "3333"
   exit_date = "444444"
   username = "5555"

现在!当我尝试将此结果发送到服务器时出现此错误:

List<Data> is not a subtype of type 'String' in type cast

我的类(class)向服务器发送数据:

class SendInformation{
  Future<bool> sendDataToServer(List<Data> list) async{
    RestData restData = RestData(data: list);

    final response = await http.post('http://sample.com',body:restData.toJson()).timeout(Duration(seconds: 60));
    if(response.statusCode ==200){
      return true;
    }else{
      return false;
    }
  }
}

我不确定，但我认为问题出在这行代码中:

restData.toJson()

对 JsonSerializable 的更新:

part 'rest_data.g.dart';

@JsonSerializable()
class RestData {
  final List<Data> data;

  RestData(this.data);

  factory RestData.fromJson(Map<String, dynamic> json) => _$RestDataFromJson(json);

  Map<String, dynamic> toJson() => _$RestDataToJson(this);
}

part 'data.g.dart';

@JsonSerializable()
class Data {
  @JsonKey(name: 'staff_id')
  String staffId;
  @JsonKey(name: 'class_id')
  String classId;
  @JsonKey(name: 'class_name')
  String className;
  @JsonKey(name: 'enter_date')
  String enterDate;
  @JsonKey(name: 'exit_date')
  String exitDate;
  @JsonKey(name: 'username')
  String username;

  Data(this.staffId, this.classId, this.className, this.enterDate, this.exitDate, this.username);

  factory Data.fromJson(Map<String, dynamic> json) => _$DataFromJson(json);
  Map<String, dynamic> toJson() => _$DataToJson(this);
}

Answer 1

import 'dart:async';
import 'dart:convert';
import 'dart:io';
import 'package:http/http.dart' as http;

class SendInformation{
  Future<bool> sendDataToServer(List<Data> list) async{
    RestData restData = RestData(data: list);

    final response = await http.post('http://sample.com',body:json.encode(restData.toJson())).timeout(Duration(seconds: 60));
    if(response.statusCode ==200){
      return true;
    }else{
      return false;
    }
  }
}

用 json.encode(Your_JSON_String) 解析你的 json